Production of Rhodomonas sp. at pilot scale under sunlight conditions

Rhodomonas sp., is an important microalga for aquaculture feed applications and gained increased research interest over the past few years. While efforts to optimise cultivation of the strain have been studied in detail under laboratory conditions, Rhodomonas sp. has never been grown in photobioreactors at large scale under outdoor light conditions. To study the industrial potential of this strain, we cultivated Rhodomonas sp. in three identical tubular photobioreactors with 200 l working volume each, located in a greenhouse using sunlight conditions only. Growth experiments were performed from February with winter light conditions (50 mol m−2 d−1) in July, representing all sunlight conditions in the Netherlands. All nutrients were supplied in surplus and temperature and pH were maintained at optimum values for growth of Rhodomonas sp., based on lab data. The total light per reactor was calculated using a ray-tracing analysis to allow calculations based on the light reaching each individual reactor. Rhodomonas sp. grew under all tested light conditions. Biomass yield on light decreased with increasing light conditions from 0.43 ± 0.21 g mol−1 to 0.18 ± 0.04 g mol−1 at 0–10 molph m−2 d−1 to 30–40 molph m−2 d−1. Biomass productivities increased with increasing light from 0.09 ± 0.04 g l−1 d−1 to 0.19 ± 0.06 g l−1 d−1, for 0–10 and 30–40 molph m−2 d−1. We obtained a 2–5 fold increase in biomass productivity compared to previous reports on Rhodomonas sp. cultivation using artificial light at large scale. Our results show that Rhodomonas sp. can be grown at pilot scale using sunlight conditions and further improvements can be reached in the future.